A printing system that performs printing by a printer based upon a raster image sent from a host computer is known in the art. Such a printer is referred to as a “host-based printer”. When a raster image in print data transmitted to the host-based printer is rasterized, draw data such as text, graphics and photographs created by an application program (referred to simply as an “application” below) running on the host computer is spooled temporarily in a virtual page memory of the host computer as a spool file (EMF data) via a rendering module [referred to as a “GDI” (Graphic Device Interface) in Microsoft's Windows (registered trademark) operating system] of the operating system, after which the spool file is read out and rasterized by a printer driver or by the rendering module of the operating system.
There is such a system (see the specification of Japanese Patent Application Laid-Open No. 2003-167701) in which draw data from within an application is spooled in a spool file of an operating system and the file is read out by a print processor and rasterized by a printer driver or by a rendering module of the operating system.
When data is rasterized into such raster-image data and the data is text data, the application outputs not only the style of a character and the character code but also coordinate information indicating the position of the character. If the data is graphic data, then the application outputs the category, such as the shape, the color and coordinate information. In the case of an image such as a photograph, the application outputs the sizes of original image and of the output destination.
The greater functionality of recent applications is accompanied by greater complexity of the data generated by the applications. Accordingly, depending upon the printer and the functions of the printer driver, there are cases where data that has been accepted from the application cannot be analyzed and rasterized to image data correctly. As a consequence, when some applications output text data and graphic data created thereby to a printer, there are instances where the data is printed after being rasterized by the application into image data conforming to the rendering resolution of the printer. If data that has been rasterized into an image is spooled using an application of this kind, the size of the spool data becomes very large and a problem which arises is that the computer hard disk and memory are put under pressure.
A similar problem is conceivable even if the application is not one that rasterizes images. With the popularization of high-resolution digital cameras in recent years, it has become possible to deal with high-resolution image data in host computers. If high-resolution image data is printed upon being pasted to the page of a document, there are instances where, depending upon the application, the original image data is output as is without being made to conform to the number of pixels of the area pasted. If the output data is spooled using such an application, the size of the spool data becomes very large and therefore the computer hard disk and memory are put under pressure. Specifically, depending upon the operating system, there are cases where a print error occurs if the size of the spool data exceeds 4 GB (gigabytes), because output size supported on the application side is exceeded, or because the hard disk does not have enough available storage capacity.
In particular, owing to the ever higher rendering resolution that accompanies improvements in printer image quality achieved in recent years, the size of spool data increases, errors occur in the application or within the spooler and data cannot be rasterized into an image normally. As a result, rendering resolution cannot be raised. This is an impediment as far an improving the image quality of a printer is concerned.